Fluid distribution systems such as underground sprinklers, irrigation systems, building fire control networks, and the like have long used fluid flow rate devices to insure equalized pressure and flow through their several branches. The equalization of flow is particularly important in hydronic systems having headers of restricted size such as power plant condensers and solar collectors. These systems typically employ fluids at relatively high temperatures passing through pipes, conduits and the like where uniform distribution of the fluid and dissipation the heat associated therewith is important for the efficient operation of the system. Additionally, fluid distribution systems having many branches require some form of constant pressure regulation to insure that the system's fluid will reach all the branches at sufficient pressure.
Constant fluid flow regulation is typically achieved through the use of orifices and/or constant rate fluid flow valves.
Orifices, while being inexpensive, limit the system with which they are associated to a relatively small range of fluid pressure variation and tend to become partially or wholly blocked by foreign particles in the fluid.
Constant rate fluid flow valves are advantageous over orifices in that they provide a constant flow rate over varying pressure differentials. Such valves are generally inserted inline with fluid distribution systems and externally on the headers of hydronic systems. These valves typically comprise a housing with an aperture passing therethrough axially with the flow of fluid in the system. A reed is affixed to the body and covers one end of the aperture to partially block the fluid flow therethrough. The reed is typically arcuate in shape and has a carefully tailored spring constant causing it to resist the pressure applied by a pressure drop across the reed in a manner which will approximate constant fluid flow over varying pressure drops. The area in which the reed meets the opening of the aperture is typically flat and thus the flow rate characteristic of the valve is controlled solely by the spring constant of the reed. Because the spring constant must be carefully tailored, the reeds typically are of a relatively large size and must be secured to the housing by means of screws and other suitable hardware. Because of this characteristic such valves are often expensive and therefore uncompetitive in many system applications. They are also physically large and are thus suitable only for systems having relatively large flow rates.